1. Field of the Invention
This invention relates to a device for driving optical parts of an optical pickup.
2. Background
An optical pickup reads information by way of irradiating a focused-information-reading laser beam onto a recording track formed in an information-recorded surface of a recording medium, and by detecting changes in the light beam reflected from the information-recorded surface. Therefore, the information reading laser beam needs to be focused at all times on the recording track, even if the surface of the recording medium deflects due to warping or the like. Therefore, the system is constituted in such a manner that focus servo control can be conducted when an objective lens, which acts to focus the laser beam, is slightly moved in a direction perpendicular to the information-recorded surface. Furthermore, since the laser beam must correctly and at all times follow the recording track, even if the recording track becomes eccentric, the system is constituted in such a manner that tracking servo control can also be conducted when the objective lens is slightly moved in the direction perpendicular to the recording track.
In order to realize the above-described movement of the objective lens, a device for driving a lens 1, shown in FIGS. 1 and 2, has been disclosed by the applicant of the present invention. In the device for driving a lens of the type described above, an objective lens 1 for irradiating a spot light beam onto a recording surface of a recording medium (omitted from the illustration) is, as shown in FIG. 1, fitted onto a holding member 2. The holding member 2 has a hollow portion 3 penetrating therethrough. In the hollow portion 3, a focusing coil 4 and two tracking coils 5 are fastened. The focusing coil 4 is secured in such a manner that the central axis thereof is parallel to the optical axis of the objective lens 1. The tracking coils 5 are attached to the outer surface of the focusing coil 4 in such a manner that the central axis of each tracking coil 5 is disposed perpendicular to the optical axis of the objective lens 1. The holding member 2, to which the focusing coil 4, tracking coils 5, and objective lens 1 are secured, is fitted to free ends of four cantilevered support members 6 which extend perpendicular to the direction of the optical axis of the objective lens 1. On the other hand, the fixed ends of the support members 6 are fastened to a base 7. Since the four support members 6 are flexible, the holding member 2 is able to move in the axial direction of the optical axis of the objective lens 1 (the direction designated by an arrow F) and in a direction perpendicular to the direction of the optical axis (the direction designated by an arrow T). This movement is with respect to the base 7.
A magnet 8 and a yoke 9 which generate a magnetic field that links the focusing coil 4 and the tracking coils 5 are inserted into the hollow portion 3 of the holding member 2 which is supported on the base 7 in such a manner that the holding member 2 is able to move in the above two directions with respect to the base 7. A magnetic circuit is formed by the magnet 8 and the yoke 9, which is preferably made of a ferromagnetic material. A single magnetic gap 10 which generates parallel flux is provided in the magnetic circuit formed by the magnet 8 and the yoke 9. The magnet 8 and the yoke 9 inserted into the hollow portion 3 are secured to a securing member (omitted from the illustration) which is secured to the base 7.
In the device for driving the lens, the structure of which is constituted as described above, the objective lens 1 with the holding membert 2 can be moved in the direction designated by the arrow F by supplying electric current to the focusing coil 4. On the other hand, the objective lens 1 with the holding member 2 can be moved in the direction designated by the arrow T by supplying electric current to the tracking coils 5.